Nectar-feeding bats of the genus Hsunycteris are endemic to the Neotropical region and currently include four recognized species: Hsunycteris thomasi, H. cadenai, H. pattoni, and H. dashe. Hsunycteris thomasi is considered a common nectar-feeding bat in Amazonia, where it is widely distributed, with presumed large subpopulations in Brazil. Based on five misidentified Hsunycteris specimens previously housed in scientific collections and recently surveyed specimens, we report eight new records that represent notable range extensions and provide the first Cytb sequence of Hsunycteris for the Atlantic Forest biome. These records include the first documentation of the genus in the Atlantic Forest biome, the Cerrado-Atlantic Forest transition zone, and the fourth record for the Cerrado biome. Among these, we present the first occurrence of the genus in the Brazilian states of Pernambuco, Alagoas, and Minas Gerais, the second occurrence in Mato Grosso, and the first record for the Cerrado of Maranhão state. Further field efforts in the northeastern Atlantic Forest allowed us to obtain tissue samples for genetic analysis, leading to the identification of a new lineage within the H. thomasi species complex in the Atlantic Forest. Phylogenetic analysis based on the Cytb gene reveals that Hsunycteris forms a monophyletic group comprising six clades. Hsunycteris dashe was recovered as a sister to a clade containing H. cadenai, H. pattoni, and three distinct lineages of H. thomasi. The H. thomasi lineages were recovered as paraphyletic, with lineage I diverging first within the clade, lineage II as a sister to H. pattoni, and lineage III as a sister to H. cadenai. Genetic distances among the H. thomasi lineages range from 7.4% to 8.6%. These results show that the specimens reported here are part of a newly recovered lineage, representing a putative new species, evincing that the diversity of the genus is higher than previously thought.